Directive transmission (also denoted directional transmission), wherein antennas may be pointed in different specific directions, is a way to improve capacity in a wireless network while also reducing interference. There are propagation conditions that require directive transmission, which may be realized by beamforming on a transmitting side to obtain good Signal to Interference-plus-Noise Ratio (SINR) conditions. Such propagation conditions arise for example in millimeter wavelength (MMW) bands, which bands may be used e.g. for wireless communication in ultra dense communication networks (UDN).
There may be a need to broadcast information to all receivers in the vicinity of a transmitter in such situations, i.e. where the radio propagation conditions require directive transmission, the directive transmission in turn requiring beamforming. A current solution is then to use beam sweeping to cover the entire sphere around the transmitter or part of this sphere. FIG. 1 illustrates this current beam sweeping. A potentially narrow transmit beam 1 is swept in every direction to cover a certain desired area 2, such as the upper sphere around the transmitter. In FIG. 1, the transmitter is part of the access node denoted AN. In the broadcasting, the transmitter transmits the same information in every direction. In this way the transmission will reach all receiving communication devices 3 located close enough in any direction around the transmitter. This approach is sometimes denoted pseudo-omni broadcasting.
Broadcast signals should reach all potential receivers within the coverage area of the transmitter, and while this type of beam sweeping is adequate for many situations, it also entails drawbacks, for example in situations where there are only a few receivers in the area. The beam sweeping then radiates energy in many directions in which there are no receivers or only seldom are receivers and a lot of radiated energy will be wasted.
Further, the broadcast signal may reach a receiver quite late as a result of this beam sweeping. Such delays are particularly adverse for time critical applications, involving time critical broadcast signals.
Another way to perform the required broadcasting could be to code the signals heavily in time and use omni-directional broadcasting during a longer period of time. However, such solution is not always possible, e.g. due to antenna configurations. This solution further entails several drawbacks such as the broadcast transmissions being more difficult for the receivers to detect since the resulting received signal will have lower power and thus be more buried in noise.